InterPro domain: IPR001486

This entry represents a group of haemoglobin-like proteins found in eubacteria, cyanobacteria, protozoa, algae and plants, but not in animals or yeast. These proteins have a truncated 2-over-2 rather than the canonical 3-over-3 alpha-helical sandwich fold [ 1 ]. They include:

• HbN (or GlbN): a truncated haemoglobin-like protein that binds oxygen cooperatively with a very high affinity and a slow dissociation rate, which may exclude it from oxygen transport. It appears to be involved in bacterial nitric oxide detoxification and in nitrosative stress [ 2 ].
• Cyanoglobin (or GlbN): a truncated haemoprotein found in cyanobacteria that has high oxygen affinity, and which appears to serve as part of a terminal oxidase, rather than as a respiratory pigment [ 3 ].
• HbO (or GlbO): a truncated haemoglobin-like protein with a lower oxygen affinity than HbN. HbO associates with the bacterial cell membrane, where it significantly increases oxygen uptake over membranes lacking this protein. HbO appears to interact with a terminal oxidase, and could participate in an oxygen/electron-transfer process that facilitates oxygen transfer during aerobic metabolism [ 4 ].
• Glb3: a nuclear-encoded truncated haemoglobin from plants that appears more closely related to HbO than HbN. Glb3 from Arabidopsis thaliana (Mouse-ear cress) exhibits an unusual concentration-independent binding of oxygen and carbon dioxide [ 5 ].

1. Structural and functional properties of hemoglobins from unicellular organisms as revealed by resonance Raman spectroscopy. J. Inorg. Biochem. 99, 72-96
2. Oxygen binding and NO scavenging properties of truncated hemoglobin, HbN, of Mycobacterium smegmatis. FEBS Lett. 580, 4031-41
3. Solution 1H NMR study of the heme cavity and folding topology of the abbreviated chain 118-residue globin from the cyanobacterium Nostoc commune. Biochemistry 39, 1389-99
4. Mycobacterium tuberculosis hemoglobin HbO associates with membranes and stimulates cellular respiration of recombinant Escherichia coli. J. Biol. Chem. 277, 15293-302
5. A hemoglobin from plants homologous to truncated hemoglobins of microorganisms. Proc. Natl. Acad. Sci. U.S.A. 98, 10119-24